Magnetostrictive vibration motor



' Sept. 30, 1969 R. ABBOTT 3,470,402

MAGNETOSTRICTIVE VIBRATION MOTOR Filed Aug. 25, 19s? 2 Sheets-Sheet 1FORCE VECTOR 'l C 6 I60 FORCE VECTOR mmmmmmm:

F/ 3 INVENTOR.

FRANK R. ABBOTT A TTOREYS Sept. 30, 1969 F. R. ABBOTT 3,470,402

MAGNETOSTRICTIVE VIBRATION MOTOR Filed Aug. 25, 1967 V 2 Sheets-Sheet qFIG.

F/Gf 5 INVENTOR. FRA NK R., ABBOTT A TTORNEYS UnitedStates Patent US.Cl. 310-26 5 Claims ABSTRACT OF THE DISCLOSURE The motor of a transducercomprises a core with two end-to-end portions of magnetostrictive metalsof, respectively, positive and negative co-efiicients of expansion. Amagnetic bias is applied to the cores and the magnetic field of thesignal current so applied to the two core portions as to, respectively,increase and decrease the lines of force in the two portions tocophasally add the elongation of the two core portions.

The invention described. herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

Background The efiiciency of conversion of electric power to acousticenergy, or vice versa, in sea water is notoriously low. Some of thefactors contributing to the low efficiency in electromagnetictransducers is short stroke, cavitation at the higher frequencies, andinsensitivity of the motor to the signal current. Further, because ofthe water environment in which transducers must operate, mechanicalruggedness and massiveness is a prerequisite, particularly where deepsubmergence is expected.

The object of this invention is to provide an improved electromagnetictransducer.

A more specific object of this invention is to provide a transducerwhich is rugged in construction, has increased travel of radiatingsurface per unit of input electrical power, and increased overallstroke.

v The objects of this invention are attained by mounting a core assemblyof magnetostrictive metals between the head piece and tail piece of thetransducer for imparting relative reciprocal motion therebetween. Thecore assembly includes two members of dissimilar metals coupled togetherend-to-end so that elongation of the two members add cophasally duringoperation to increase the displacement of the headpiece with respect tothe tail piece. The two members consist of magnetostrictive metals of,respectively, positive and negative coefiicients of expansion and areprovided with a unique magnet for biasing the magnetic field in the twoportions. A coil for signal current is so coupled to the two-piece coreas to, respectively, add to and subtract from the magnetic lines offorce in the two members to cophasally expand or contract two members.Transducers thus constructed are particularly rugged and have increasedtravel of radiating surface per unit of input of electrical power and anincreased overall length of stroke.

Other objects and features of this invention will become apparent tothose skilled in the art by referring to the preferred embodimentdescribed in the following specification and shown in the accompanyingdrawings in which:

FIGS. 1 and 2 are plan and elevational views of the preferred embodimentof this invention.

FIG. 3 is a plan view of an alternative embodiment of this invention,

"ice

FIG. 4 is a partial mechanical plan view of one actual transducerembodying this invention, and

FIG. 5 is an alternative actual transducer embodying the principles ofthis invention.

The motor or active portion of the transducer of this inventioncomprises the core 10 shown in FIGS. 1 and 2 which is generally of the 0type. The magnetic circuit is generally rectangular in shape, is closedand has no air gap. The elongated legs 6 and 7 of the core are generallylonger than the transverse arms 8 and 9 of the core. Intermediate theends of and between the legs 6 and 7 is inserted the permanentpolarizing magnet 16. The pole polarizing magnet extends diagonallyacross the loop and the faces at the ends of the magnet are of oppositepolarity and are machined to snugly fit between the inner surfaces ofthe legs 6 and 7 to impart to the core 10 a magnetic bias. The magneticlines of force 16a and 16b of magnet 16 extend, respectively, inclockwise and counter clockwise directions through the two halves of.the core. The level of the magnetic bias is so selected as to maximizepermeability.

Closely inductively coupled to the core is a signal coil. The coil ispreferably although not necessarily divided into equal parts and woundon the two halves of the core on either side of the biasing magnet 16.When the two halves are U-shaped, as in FIG. 1, the coil may be wound oneach leg as at 18A, 18B, 18C, and 18D, all connected in series orparallel aiding. The lines of force 18 in the core encircle the entirecore in the clockwise direction as shown. The permeability of the magnet16 is relatively low compared to the permeability of the core 10, andhence need not be considered as a short circuiting path for lines 18. Itappears now that the lines of force 18 produced by signals are in thesame direction as bias lines 16b in one half of the core but are opposedto the bias lines of force 16a in the other half of the core. This meansthat a change in signal current always produces a decrease in field inone-half of the core and an increase in the field in the other half ofthe core.

The next important feature disclosed in the FIG. 1 resides in the factthat the core metal on one side of the bias magnet is of amagnetostrictive alloy which has a positive coefiicient of expansionwhereas the other half of the core is of magnetostrictive metal with anegative coefficient of expansion. In operation, then, the end-toendportions of the legs of the core both expand lengthwise, cophasally,with increased signal current and both contract with decreased signalcurrent. The coil must, of course, be properly polarized with respect tothe the biasing magnet.

Preferably, the core 10 is laminated, and conveniently the two halves ofthe core are U-shaped stampings. In the interest of reduced reluctanceat the abutting ends of the leg portions of dissimilar metals, thestampings are overlapped a distance approximately equal to the width ofthe biasing magnet 16. One leg of each U-shaped stamping may be cutshorter than the other leg, and each lamination is laid down so that ashort leg abuts the end of a long leg. Thus, the long legs of successivelaminations can be made to overlap. The ends of the U-shaped stampingsthus interleaved are substantially inseparable and indestructible whenjoined by the customary adhesive. Preferably, the contacting surfaces ofthe permanent magnet 16 and the inner surfaces of the laminated core 10are precisely machined to size and polished and the core 16 driven intoplace.

As stated, the coefiicient of expansion of the two magnetostrictivemetals of the core are positive and negative, respectively. While manymagnetic alloys are available on the market, good results have beenobtained by forming the stampings of one core portion from 99% nickeliron while the other core portion is 50% nickel iron.

a The specific percentages of constituents in the alloys is notcritical. The two core materials used successfully comprisedcommercially obtainable Permalloy 45 and Permalloy 90. Both alloys havehigh permeability and low hysteresis loss as well as relatively highcoefiicients of expansion. Desirably, the permanent magnet 16 is ofalnico which is capable of high magnetization and yet has relativelyhigh magnetic reluctance. With optimum magnetic bias, the alternatingsignal current required for the transducer is small. The magneticallysoft laminations are mechanically resistant to fracture while themoderately brittle alnico magnet 16 is protected from rough handling andshock by the laminations. It has been found that cracks in the alnicohave little effect on the operation of the transducer.

In FIG. 4 is shown a heavy duty transducer presently known as AN/SQS-26embodying the features of the motor of FIG. 1. The core portions 6-7-8and 6-79 are laminated and joined end-to-end as in FIG. 1. Where thelaminations are interleaved, the permanent alnico magnet 16 is inserted.The signal coil 18B and 18D are coupled to the two legs of core. Thetransverse arm portion 19 of the core bears against the tail piece 30while the transverse arms 8 is seated in the head piece 32. Tension rods34 extend between the tail and head piece to hold the assembly togetherin one unitary indestructable unit. Casing 36 enclosing the transducermay contain pressure release material and transformer oil, not shown.

In FIG. 5 the transducer AN/BQS-6 also incorporates the features ofFIG. 1. The general configuration of the core stampings in FIGS. 4 and 5are substantially alike. If desired, the signal coils 18A and 18C may becoupled to the core to supplement the coils 18B and 18D. In either casea capacitor within the casing of the transducer may be added to provideelectrical resonance at the desired frequency. A capacitor for thetransducers of FIGS. 4 and 5 was selected for electrical resonance at3.5 kilocycles per second.

In FIG. 3 the magnetostrictive portions of the core are laid out toprotect the windings from mechanical damage. Here, the two end-to-endlegs 40 and 41 of dissimilar magnetostrictive alloys are each wound withsignal coils 42 and 43. The magnetic circuit is split and completedthrough the armatures 44 and 45 while the biasing permanent magnetacross the center of the core loop is in two parts 46 and 47. Thecophasal contraction and expansion of the cores 40 and and 41 inresponse to signal currents in coils 42 and 43 is the same as in FIG. 1.

What is claimed is:

1. A transducer comprising:

a tail piece, a head piece and a core assembly of magnetostrictivemetals, said core assembly being connected between the head and tailpieces for imparting reciprocal motion to the head piece with referenceto the tail piece,

said core assembly including two substantially straight metal membersaligned and disposed end-to-end between said head and tail pieces,

said two members consisting of magnetostrictive metals of respectively,positive and negative coefiicients of expansion, and

coil means for signal current so coupled to said two core members as to,respectively, increase and decrease the magnetic field in said twomembers to cophasally expand and contract said two members.

2. The transducer defined in claim 1 further comprismg:

means for establishing a predetermined static magnetic bias in said coreassembly to maximize the magnetic permeability of said core assembly.

3. In the transducer of claim 2 said bias means including a magnet withpole faces so disposed with respect to the magnetic circuit of said coreassembly as to oppositely magnetically polarize said twomagnetostrictive members.

4. A transducer comprising:

a magnetic core having magnetostrictive characteristics, said core beinga closed loop having two elongated parallel legs and relatively shorttransverse arms,

a coil for signal current coupled to magnetic circuit of said closedloop,

a polarized biasing magnet extending diagonally across said core loopbetween intermediate portions of said parallel legs for establishingmagnetic lines of force extending, respectively, in a clockwise and acounterclockwise direction to, respectively, add to and subtract fromthe lines of force of the current of said signal coil, and

the magnetostrictive coefiicient of expansion of the portions of saidcore on opposite sides of said biasing magnet being, respectively,positive and negative so that both of said portions elongate in phasewith change in signal current.

5. In the transducer defined in claim 4, the mentioned portions of saidcore having dissimilar coefiicients each being laminated, the stampingsof each lamination being U-shape and the ends of the stampings beinginterleaved to reduce magnetic reluctance.

References Cited UNITED STATES PATENTS 2,411,911 12/1946 Turner 31026 X2,433,337 12/1947 Bozorth 340--11 2,842,689 7/1958 Harris 310263,007,063 10/1961 Harris 31026 MILTON O. HIRSHFIELD, Primary Examiner D.F. DUGGAN, Assistant Examiner US. Cl. X.R.

